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RFC 826

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Network Working Group
Request For Comments: 826

David C. Plummer
(DCP@MIT-MC)
November 1982

### An Ethernet Address Resolution Protocol

-- or --
Converting Network Protocol Addresses
to 48.bit Ethernet Address
for Transmission on
Ethernet Hardware

#### Abstract

The implementation of protocol P on a sending host S decides, through protocol P's routing mechanism, that it wants to transmit to a target host T located some place on a connected piece of 10Mbit Ethernet cable. To actually transmit the Ethernet packet a 48.bit Ethernet address must be generated. The addresses of hosts within protocol P are not always compatible with the corresponding Ethernet address (being different lengths or values). Presented here is a protocol that allows dynamic distribution of the information needed to build tables to translate an address A in protocol P's address space into a 48.bit Ethernet address.

Generalizations have been made which allow the protocol to be used for non-10Mbit Ethernet hardware. Some packet radio networks are examples of such hardware.

#### Table of Contents

The Problem
Motivation
Definitions
Packet format
Packet Generation
Packet Reception
Why is it done this way??
Network monitoring and debugging
An Example
Related issue

Original text document

#### Notes

The protocol proposed here is the result of a great deal of discussion with several other people, most notably J. Noel Chiappa, Yogen Dalal, and James E. Kulp, and helpful comments from David Moon.

[The purpose of this RFC is to present a method of Converting Protocol Addresses (e.g., IP addresses) to Local Network Addresses (e.g., Ethernet addresses). This is a issue of general concern in the ARPA Internet community at this time. The method proposed here is presented for your consideration and comment. This is not the specification of a Internet Standard.]

This protocol was originally designed for the DEC/Intel/Xerox 10Mbit Ethernet. It has been generalized to allow it to be used for other types of networks. Much of the discussion will be directed toward the 10Mbit Ethernet. Generalizations, where applicable, will follow the Ethernet-specific discussion.

DOD Internet Protocol will be referred to as Internet.

Numbers here are in the Ethernet standard, which is high byte first. This is the opposite of the byte addressing of machines such as PDP-11s and VAXes. Therefore, special care must be taken with the opcode field (ar$op) described below.

An agreed upon authority is needed to manage hardware name space values (see below). Until an official authority exists, requests should be submitted to

David C. Plummer
Symbolics, Inc.
243 Vassar Street
Cambridge, Massachusetts 02139

Alternatively, network mail can be sent to DCP@MIT-MC.

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Connected: An Internet Encyclopedia
RFC 826